Arsenical insecticide safened with zinc sulfite



Patented Feb. 6, 1951 zinc SULFITE Alexander A. Nikitin, College Park,Ga, aslignor to Tennessee Copper Company, New York, N. Y a corporationof New Jersey No Drawing. Application April 22, 1948,

Serial No. 22,717 Y 6 Claims. (01. 167 15) This invention relates toimprovements in insecticidal compositions, and this application is acontinuation in part of my prior applications Serial No..606,879, filedJuly 24, 1945, now abandoned, and Serial No. 9,391, filed February 18,1948.

The use of various forms of zinc in fungicidal and insecticidalcompositions has been proposed heretofore. For example, U. S. Patent No.2,-

051,910 proposes to use a complex copper-zinc silicate as a fungicide,the zinc being added to. improve the physical properties of the silicatefor this purpose. U. S. Patent No. 2,225,867 asserts that zinc oxideacts synergistically with copper oxide when the two are mixed and usedfor fungicidal purposes, whereas synergistic action is not obtained withother zinc compounds including zinc carbonate, zinc silicate and zincoxalate. U. S. Patent No. 2,376,740 also proposes the use of basic zincsulphate as a safener in calcium arsenate insecticides.

Apart from such physical and activating effects, zinc ion per se isbeneficial for protection plus lime). basic copper sulphate, and basicagainst pests. However, most zinc salts are not suitable for use infungicidal or insecticidal compositions. Soluble zinc salts such as zincsulphate cause a severe injury to foliage. This fact is recognized inPatent No. 2,376,740 and also in U. S. Patent No. 1,905,532 wherein zincis proposed as an immunizing agent against certain forms of blight. Inboth cases the soluble zinc sulphate is accordingly converted toinsoluble basic zinc sulphate by reaction with an excess of lime. Basiczinc salts such as basic zinc sulphate do not injure the plant, but onthe other hand they are relatively ineffective as fungicides becausethey are so insoluble that they do not furnish the required amount ofzinc ion.

It has been found that the zinc sulphite is very beneficial when used onplants. The chief value of zinc sulphite is that it furnishes zinc ioiigradually as a result of the slow oxidation of zinc sulphite to zincsulphate upon its exposure to atmospheric action after the compound hasbeen used in the field. Thus the fungicidal effectiveness of zincsulphite has been found to be much greater than that of basic zincsulphate (zinc- Bordeaux mixture) in laboratory tests on toxicity tospore germination and in field tests on control of potato blight andpecan rosette disease. On the other hand, zinc sulphite is not only safeto use on plants but also is highly beneficial for plant growth. Forexample, when tested in the field against Bordeaux mixture (coppersulphate plus lime), zinc-Bordeaux mixture (zinc sulphate coppersulphate chloride, zinc sulphite proved far superior as to increase ofvine weight and increase of moisture content of the tubers.

In addition to its highly beneficial effects mentioned above, zincsulphite has a special value for use with copper fungicides and/orarsenical insecticides. As pointed out in my prior applications, it isknown that soluble copper and soluble arsenic are injurious to fruit andfoliage. For this reason copper and arsenic used for fungicidal andinsecticidal purposes are used in relativelyinsoluble forms, butnevertheless soluble fractions liberated by atmospheric action and byinteraction with other ingredients of the fungicidal composition maycause injury to the plant. I

My prior application Serial No. 9,321 is direc particularly tofungicides containing copper with or without organic' fungicides orinsecticides, arsenicals, etc. The present application, on the otherhand, is directed particularly to the use of arsenical insecticides inthe absence of copper. The arsenicals commonly used for such purposesinclude lead arsenate which is usedchiefly for fruits such as apples,cherries and peaches, and tricalcium arsenate which is used chiefly forvegetables such as tomatoes. Although such arsenicals are relativelyinsoluble, nevertheless injury to the plant often results fromliberation of soluble arsenical fractions on exposure of such relativelyinsoluble arsenicals to the atmosphere.

The use of zinc sulphate to prevent such injurious eifects of arsenicalshas been tried without success due to the high solubility of this zincsalt. The use of lime with zinc sulphate forms a basic zinc sulphate soinsoluble that it does not protect the plant against such injuries.Other zinc salts such as zinc phosphate and zinc oxalate are tooinsoluble in water to provide protection.

' Zinc sulphite, in addition to its beneficial effects mentioned above,is the only zinc salt as far as I know which gives the desiredprotection against arsenical injury to the plant as shown by laboratoryand field tests. its effectiveness in this respect is attributed to thefact that it furnishes a sufficient concentration of zinc ion to exert asubstantial buflering eifect.

The eifectiveness of 'zinc sulphite in protecting plants againstarsenical injuries can be further explained as follows. As stated above,soluble zinc salts such as zinc sulphate can not be used because ofsevere injury to fruit and foliage. On the other hand, basic zinc saltssuch as obtained by the combination of zinc sulphate and lime aresoluble zinc secured from basic zinc salts does not give the desiredprotection in many cases, whereas ainc sulphite is much more eifectiveas explained above.

Another important advantage of the use of zinc sulphite with arsenicalsis that the zinc sulphite is compatible with virtually all organicinsecticides and fungicides and does not require the addition ofalkaline materials such as lime, as is the case with other soluble zincsalts. It has been found that in most cases alkaline materials such aslime or sodium or potassium carbonates ture is used. Furthermore it willbe understood that the amount of protective action obtained increasesprogressively as the amount of zinc sulphite is increased up to amaximumamount be yond which no further increase of protective action isobtained. Some degree of protective action will be obtained with onlyvery small amounts of zinc sulphite. but as a rule the minimum amountshould be about 30% of the amount of arsenical. In the case of lessinjurious arsenicals such as lead arsenate, about 30-40% zinc sulphitewill usually be sufficient, but in the case of more injurious arsenicalssuch as tricalcium aror hydroxides have an adverse effect on theseorganic materials, reducing the effectiveness of organic fungicides suchas disodium ethylene bisdithiocarbamate (Dithane) and decomposingorganic insecticides such as pyrethrum, rotenone and nicotine products.Thus in the case of combination treatments using arsenicals with organicfungicides and/or insecticides. the use of zinc sulpliate. plus lime ishighly undesirable, but zinc sulphite can be used to reduce arsenicalinjuries without adverse eiiects on the organic materials.

The protective action of zinc sulphite against arsenical injuries asmentioned above is highly eifective. However, the zinc sulphite has atendency to oxidize to zinc sulphate, decreasing the amount of zincsulphite available for protective action, and forming increasing amountsof zinc sulphate which in turn increases the solubility of arsenicals.The soluble zinc sulphate itself and the soluble arsenic as well areinjurious to fruit and foliage, and the injury may become severe whenthe zinc sulphite is exposed to atmospheric action for considerableperiods or when the composition is held in storage before use. In suchcases the protective action of the zinc sulphite may be prolonged by theuse of aluminum oxide or iron oxide which greatly diminishes theoxidation of zinc sulphite to zinc sulphate and minimizes the injuriesto fruit and foliage.

It should be noted that the aluminum oxide or iron oxide when usedalone, i. e., without zinc senate, larger amounts of zinc sulphite -upto 60-70% are desirable. Still larger amounts can be used, but usuallyto no advantage because no additional protection will be obtained.

When aluminum oxide is used to prolong the protective action of the zincsulphite. the ratio of oxide to zinc sulphite may also vary within widelimits. However, it will usually be undesirable for this ratio to exceed1:4 (oxide to zinc sulphlte) as increases in the proportion of oxidebeyond this ratio will not increase the protection afforded the zincsulphite. The ratio of oxide may be decreased to as little as 1:14 andsubstantial benefit still obtained. The corresponding ratios in the caseof iron oxide will depend on the composition of the oxide used. Forexample, in the case of iron oxide consisting of about one-third ferrousoxide and two-thirds ferric oxide, the ratio should be approximately thesame as in the case of aluminum oxide.

sulphite, does not have beneficial value in relation to arsenicalinjuries. Its value lies in prolonging the eflectiveness of the zincsulphite by minimizing its tendency to oxidize to zinc sulphate. Thisprotective action of aluminium oxide, iron oxide, or a mixture of thesetwo substances is most likely due to a buffering action. since: aluminumoxide or iron oxide has a neutral reaction; that is, their suspension inwater has a pH of about 7 and neither aluminum oxide nor iron oxidereacts readily with common salts, including zinc sulphite. Hence it willbe understood that the oxide is not necessary but is desirable toprolong the effectiveness of the zinc sulphite: after application to theplant and especially when the composition is stored for long periodsbefore use.

The amount of zinc sulphite to be used may vary considerably. It dependsmainly on the amount of arsenical used but will vary according to thetype of arsenical, the character of the inert diluents used in the dustor spray, and also the type of plant on which the dust or spray mix- 75used in combination with calcium arsenate and (1) 3 lbs. lead arsenate.(PbH A804) 1 lb. zinc sulphite 0.25 lb. aluminum oxide (2) 3 lbs.tricalcium arsenate 2 lbs. zinc sulphite 0.5 lbs. aluminum oxide Aspreviously stated, combinations of zinc sulphite with arsenicals such asindicated by the above examples can be used with organic insecti-- cidesand/or fungicides as may be desired. For example. DDT and lead arsenateare used for the control of curculio on peaches and have also been usedon apples with surprising eifectiveness against coddling moth larvae. Insuch cases the combined treatment with DDT and lead arsenate may be usedwith the addition of zinc sulphite which serves as a buffer againstarsenical injury and reduces damage to twigs and foliage. Thecombination of lead arsenate and nicotine sulphate is recommended ingeneral summer fruit spray schedules, and zinc sulphite may be used insuch combinations to reduce arsenical injury. Zince sulphite is alsocompatible with nicotinebentonite (Black Leaf and may be usedeffectively to render lead arsenate safer in lead arsenate-nicotine'treatments.

The fact that zinc sulphite does not require the addition of lime makesit advantageous for use in the above combinations of arsenicals andorganic insecticides as compared with zinc sulphate plus lime whichoften causes deleterious eiiects. The same advantage is obtained by theaddition of zinc sulphite to combinations of arsenicals with organicfungicides. For example, disodium ethylene bisdithlocarbamate (Dithane)is commonly zinc sulphatelime for the control of tomato diseases andinsects. By using zinc sulphite, the

need for lime is eliminated. Thus the deleterious effects of lime on theorganic insecticides are avoided, and the zinc sulphite also serves as abuffer against soluble arsenic in the arsenical insecticides.

In most cases it will be desirable to mix the zinc sulphite with theother ingredients of the composition so that all may be applied to theplant simultaneously in a single dusting or spraying operation. It ispossible, however, to apply the zinc sulphite to the plant separately.In this case the zinc sulphite application may either precede or followthe arsenical application but the two applications should be madesubstantially simultaneously; i. e., no more than one or two days shouldbe permitted to intervene if the above mentioned benefits of conjointuse are to be obtained.

It will also be understood that the proportions of the above examplesare only illustrative and may vary widely under difierent conditions.Hence reference should be had to the appended claims for a definition ofthe limits of the invention.

What is claimed is:

1. A composition for application to plant foliage and fruit for thecontrol of pests which contains zinc sulphite together with an arsenicalinsecticide.

2. A composition for application to plant foliage and fruit for thecontrol of pests which contains zinc sulphite and a protective oxideselected from the group consisting of aluminum and iron oxides togetherwith an arsenical insecticide.

3. A composition for application to plant foli- 6 age and fruit for thecontrol of pests which contains zinc sulphite together with an arsenicalinsecticide and an organic fungicide.

4. A composition for application to plant foliage and fruit for thecontrol of pests which contains zinc sulphite together with an arsenicalinsecticide and an organic insecticide.

5. A composition for application to plant foliage and fruit for thecontrol of pests which contains zinc sulphite and a protective oxideselected from the group consisting of aluminum and iron oxides togetherwith an arsenical insecticide and an organic fungicide.

6. A composition for application to plant foliage and fruit for thecontrol of pests which contains zinc sulphite and a protective oxideselected from the group consistingof aluminum and iron oxides togetherwith an arsenical insecticide and an organic insecticide.

ALEXANDER A. NIKITIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

' OTHER REFERENCES Heuberger et al., Del. Agr. Expt. Sta. Pamphlet 10,1944, obtained through Frear, Chemistry of Insecticides, Fungicides, andHerbicides, Van Nostrand Co. Inc.,' New York (1948) page 266.

1. A COMPOSITION FOR APPLICATION TO PLANT FOLIAGE AND FRUIT FOR THECONTROL OF PESTS WHICH CONTAINS ZINC SULPHITE TOGETHER WITH AN ARSENICALINSECTICIDE.